661865 has 8 divisors (see below), whose sum is σ = 836160. Its totient is φ = 501552.

The previous prime is 661849. The next prime is 661873. The reversal of 661865 is 568166.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 661865 - 2⁴ = 661849 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3389 + ... + 3578.

It is an arithmetic number, because the mean of its divisors is an integer number (104520).

2⁶⁶¹⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

661865 is a deficient number, since it is larger than the sum of its proper divisors (174295).

661865 is a wasteful number, since it uses less digits than its factorization.

661865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6991.

The product of its digits is 8640, while the sum is 32.

The square root of 661865 is about 813.5508588896. The cubic root of 661865 is about 87.1478088073.

The spelling of 661865 in words is "six hundred sixty-one thousand, eight hundred sixty-five".